This invention relates to biodegradable lubricants, and more particularly to semi-fluid grease compositions based on synthetic or natural base oils including esters and glycols and thickener systems including a naturally occurring phosphatide extended performance and anti-wear agent designed to be biodegradable for environmentally sensitive applications and such compositions having a specific gravity greater than or equal to 1.0 for maritime, inland, coastal waterways, water purification and waste water treatment applications.
There is a continuing need to provide lubricant compositions which are biodegradable. This is particularly true with respect to lubricants for bearings and other marine applications and 2-stroke engines. These engines are often small gasoline engines used in recreational vehicles, such as motorboats, mono-skis for water use, snowmobiles and in lawn equipment. Thus, all such uses are in sensitive environments subject to pollution. Absent an acceptable biodegradability level, exhaust and leakage of lubricants tend to pollute forests, rivers, lakes and other waterways.
A stem tube bearing is one of the most important bearing in a propeller driven ship and is often the subject of controversy. It is reported that failures of oil lubricated metal propeller shafts have a failure rate as high as 10% on ships having tailshafts equal to or greater than 600 mm diameter. The failures are associated with seal failure resulting in the spreading of oil onto the water. Stern tube lubricants have been designed to lubricate the load carrying bearings for marine vessel propeller shafts. These mineral oil formulations cause a “sheen” or iridescent appearance on the surface of water upon leakage from a stern tube seal. The mineral oil and additives that augment the performance of these types of lubricants are not readily biodegradable and usually environmentally harmful.
In water purification and wastewater treatment facilities, several pieces of machinery are lubricated with biodegradable lubricants. However these lubricants have a density lower than that of water, or a specific gravity less than 1.0 at 60° F. (15.6° C.). These lighter than water lubricants float on the surface and may cause a surface sheen. Removal of the lubricant requires expensive skimming equipment further downstream.
Biodegradability is measured pursuant to the OECD 301B test known as the Modified Sturm test and was adopted by the Organization for Economic Cooperation Development in 1979. The test has been adopted as a European Union standard for biodegradability as test standard EU C.4-C. The biodegradability test involves the measurement of the amount of CO2 produced by the test compound, which is, in turn, expressed as a percent of the theoretical CO2 the compound could produce calculated from the carbon content of the test compound. The test is performed to measure released CO2 trapped as BaCO3 and is well known to those in the art and will not be set forth herein in detail. Generally, lubricants having a biodegradability of over 60% pursuant to the OECD 301B test are considered to have acceptable biodegradability characteristics. By way of comparison, mineral oils in the same test show typically results of between 20 to 30 percent.
Present biodegradable basestocks based on branched chain synthetic esters and lubricants formed therefrom are disclosed in U.S. Pat. No. 5,681,800. Here, branched chain fatty acids provide the desired viscometrics, low temperature properties, lubricity, biodegradability and solubility of additives therein. A 2-stroke engine lubricant based on polyneopentyl polyol ester lubricants is described in U.S. Pat. No. 6,551,968. These oils and lubricants that float on the water's surface adhere to the skin, fur and feathers of marine life and birds, causing injury to animals and plants. This commonly recognized iridescent film also tends to reduce transmission of oxygen into the water, thereby endangering marine life.
Overbased calcium sulfonate based grease thickening systems are also well known in the art. These are disclosed in U.S. Pat. Nos. 4,560,489 and 5,308,514. These greases usually contain calcium borate, making these systems not desirable for environmentally sensitive uses.
Various known lubricants having biodegradable properties are available, leakage tends to cause the lubricants to collect on the surface of the water. Accordingly, it is desirable to provide a biodegradable lubricant suitable for environmentally sensitive applicants and that will not collect on the surface of water and is readily biodegradable by aquatic organisms and overcomes common environmental hazards associated with lubricants.